lm25017

LM25017 SNVS951–DECEMBER2012 LM2501748V,650mA Constant On-Time Synchronous Buck RegulatorCheck for Samples:LM25017FEATURES•Frequency Adjustable to1MHz•Adjustable Undervoltage Lockout(UVLO)•Integrated48V,High and Low Side Switches•Remote Shutdown•No Schottky Required•Thermal Shutdown•Constant On-time Control•No Loop Compensation RequiredAPPLICATIONS•Ultra-Fast Transient Response•Industrial Equipments•Nearly Constant Operating Frequency•Smart Power Meters•Intelligent Peak Current Limit•Telecommunication Systems•Adjustable Output Voltage from1.225V•Isolated Bias Supply•Precision2%Feedback ReferenceDESCRIPTIONThe LM25017is a48V,650mA synchronous step-down regulator with integrated high side and low side MOSFETs.The constant-on-time(COT)control scheme employed in the LM25017requires no loop compensation,provides excellent transient response,and enables very low step-down ratios.The on-time varies inversely with the input voltage resulting in nearly constant frequency over the input voltage range.A high voltage startup regulator provides bias power for internal operation of the IC and for integrated gate drivers.A peak current limit circuit protects against overload conditions.The undervoltage lockout(UVLO)circuit allows the input undervoltage threshold and hysteresis to be independently programmed.Other protection features include thermal shutdown and bias supply undervoltage lockout(V CC UVLO).The LM25017is available in LLP-8and PSOP-8plastic packages.Packages•LLP-8•PSOP-8Typical ApplicationPlease be aware that an important notice concerning availability,standard warranty,and use in critical applications ofTexas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.All trademarks are the property of their respective owners.PRODUCTION DATA information is current as of publication date.Copyright©2012,Texas Instruments Incorporated Products conform to specifications per the terms of the TexasInstruments standard warranty.Production processing does notnecessarily include testing of all parameters.UVLO 3RON4RTN 1VIN 28 SW7 BST6 VCC5 FBPSOP-8Exp PadLM25017SNVS951–DECEMBER 2012Connection DiagramFigure 1.Top View (Connect Exposed Pad to RTN)Figure 2.Top View (Connect Exposed Pad to RTN)Pin FunctionsTable 1.Pin DescriptionsPin Name DescriptionApplication Information1RTN Ground Ground connection of the integrated circuit.2V IN Input VoltageOperating input range is 9V to 48V.3UVLOInput Pin of Undervoltage ComparatorResistor divider from V IN to UVLO to GND programs the undervoltage detection threshold.An internal current source is enabled when UVLO is above 1.225V to provide hysteresis.When UVLO pin is pulled below 0.66V externally,the parts goes in shutdown mode.4R ONOn-Time ControlA resistor between this pin and V IN sets the switch on-time as a function of V IN .Minimum recommended on-time is 100ns at max input voltage.5FB FeedbackThis pin is connected to the inverting input of the internal regulation comparator.The regulation level is 1.225V.6V CCOutput from the Internal High Voltage Series Pass The internal V CC regulator provides bias supply for the Regulator.Regulated at 7.6V gate drivers and other internal circuitry.A 1.0μF decoupling capacitor is recommended.7BSTBootstrap CapacitorAn external capacitor is required between the BST and SW pins (0.01μF ceramic).The BST pin capacitor is charged by the V CC regulator through an internal diode when the SW pin is low.8SW Switching Node Power switching node.Connect to the output inductor and bootstrap capacitor.EPExposed PadExposed pad must be connected to RTN pin.Connect to system ground plane on application board for reduced thermal resistance.These devices have limited built-in ESD protection.The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.2Submit Documentation FeedbackCopyright ©2012,Texas Instruments IncorporatedProduct Folder Links:LM25017LM25017 SNVS951–DECEMBER2012Absolute Maximum Ratings(1)V IN,UVLO to RTN-0.3V to53VSW to RTN-1.5V to V IN+0.3VBST to V CC53VBST to SW13VR ON to RTN-0.3V to53VV CC to RTN-0.3V to13VFB to RTN-0.3V to5VESD Rating(Human Body Model(2)2kVLead Temperature(3)200°CStorage Temperature Range-55°C to+150°C(1)Absolute Maximum Ratings are limits beyond which damage to the device may occur.Operating Ratings are conditions under whichoperation of the device is intended to be functional.For specifications and test conditions,see the Electrical Characteristics.The RTN pin is the GND reference electrically connected to the substrate.(2)The human body model is a100pF capacitor discharged through a1.5kΩresistor into each pin.(3)For detailed information on soldering plastic PSOP package,refer to the Packaging Data Book available from National SemiconductorCorporation.Max solder time not to exceed4seconds.Operating Ratings(1)V IN Voltage9V to48V Operating Junction Temperature−40°C to+125°C (1)Absolute Maximum Ratings are limits beyond which damage to the device may occur.Operating Ratings are conditions under whichoperation of the device is intended to be functional.For specifications and test conditions,see the Electrical Characteristics.The RTN pin is the GND reference electrically connected to the substrate.Copyright©2012,Texas Instruments Incorporated Submit Documentation Feedback3Product Folder Links:LM25017LM25017SNVS951–Electrical CharacteristicsSpecifications with standard typeface are for T J=25°C,and those with boldface type apply over full Operating Junction Temperature range.V IN=48V,unless otherwise stated.See(1).Symbol Parameter Conditions Min Typ Max UnitsV CC SupplyV CC Reg V CC Regulator Output V IN=48V,I CC=20mA 6.257.68.55V V CC Current Limit V IN=48V(2)26mAV CC Undervoltage Lockout Voltage 4.15 4.5 4.9V(V CC increasing)V CC Undervoltage Hysteresis300mVV CC Drop Out Voltage V IN=9V,I CC=20mA 2.3VI IN Operating Current Non-Switching,FB=3V 1.75mAI IN Shutdown Current UVLO=0V50225µA Switch CharacteristicsBuck Switch R DS(ON)I TEST=200mA,BST-SW=0.8 1.8Ω7VSynchronous R DS(ON)I TEST=200mA0.451ΩGate Drive UVLO V BST−V SW Rising 2.43 3.6VGate Drive UVLO Hysteresis260mV Current LimitCurrent Limit Threshold0.7 1.02 1.3ACurrent Limit Response Time Time to Switch Off150nsOFF-Time Generator(Test1)FB=0.1V,V IN=48V12µsOFF-Time Generator(Test2)FB=1.0V,V IN=48V 2.5µsOn-Time GeneratorT ON Test1V IN=32V,R ON=100k270350460nsT ON Test2V IN=48V,R ON=100k188250336nsT ON Test4V IN=10V,R ON=250k188032004425ns Minimum Off-TimeMinimum Off-Timer FB=0V144ns Regulation and Overvoltage ComparatorsFB Regulation Level Internal Reference Trip Point 1.2 1.225 1.25Vfor Switch ONFB Overvoltage Threshold Trip Point for Switch OFF 1.62VFB Bias Current60nA Undervoltage Sensing FunctionUV Threshold UV Rising 1.19 1.225 1.26VUV Hysteresis Input Current UV=2.5V-10-20-29µARemote Shutdown Threshold Voltage at UVLO Falling0.320.66VRemote Shutdown Hysteresis110mV Thermal ShutdownTsd Thermal Shutdown Temperature165°C Thermal Shutdown Hysteresis20°C Thermal ResistanceJunction to Ambient PSOP-840°C/WθJALLP-840°C/W(1)All electrical characteristics having room temperature limits are tested during production at T A=25°C.All hot and cold limits arespecified by correlating the electrical characteristics to process and temperature variations and applying statistical process control. (2)V CC provides self bias for the internal gate drive and control circuits.Device thermal limitations limit external loading.4Submit Documentation Feedback Copyright©2012,Texas Instruments IncorporatedProduct Folder Links:LM25017LM25017 SNVS951–DECEMBER2012Typical Performance CharacteristicsFigure4.V CC vs V INFigure5.V CC vs I CCCopyright©2012,Texas Instruments Incorporated Submit Documentation Feedback5Product Folder Links:LM25017LM25017SNVS951– Typical Performance Characteristics(continued)Figure7.T ON vs V IN and R ONFigure8.T OFF(I LIM)vs V FB and V IN6Submit Documentation Feedback Copyright©2012,Texas Instruments IncorporatedProduct Folder Links:LM25017LM25017 SNVS951–DECEMBER2012 Typical Performance Characteristics(continued)Figure9.I IN vs V IN(Operating,Non Switching)Figure10.I IN vs V IN(Shutdown)Figure11.Switching Frequency vs V INCopyright©2012,Texas Instruments Incorporated Submit Documentation Feedback7Product Folder Links:LM25017FBV INV CCSWRTNBSTR LM25017SNVS951–DECEMBER 2012Block DiagramFigure 12.Functional Block DiagramFunctional DescriptionThe LM25017step-down switching regulator features all the functions needed to implement a low cost,efficient,buck converter capable of supplying up to 650mA to the load.This high voltage regulator contains 48V,N-channel buck and synchronous switches,is easy to implement,and is provided in thermally enhanced PSOP-8and LLP-8packages.The regulator operation is based on a constant on-time control scheme using an on-time inversely proportional to V IN .This control scheme does not require loop compensation.The current limit is implemented with a forced off-time inversely proportional to V OUT .This scheme ensures short circuit protection while providing minimum foldback.The simplified block diagram of the LM25017is shown in ,Functional Block Diagram.The LM25017can be applied in numerous applications to efficiently regulate down higher voltages.This regulator is well suited for 12V and 24V rails.Protection features include:thermal shutdown,Undervoltage Lockout (UVLO),minimum forced off-time,and an intelligent current limit.Control OverviewThe LM25017buck regulator employs a control principle based on a comparator and a one-shot on-timer,with the output voltage feedback (FB)compared to an internal reference (1.225V).If the FB voltage is below the reference the internal buck switch is turned on for the one-shot timer period,which is a function of the input voltage and the programming resistor (R ON ).Following the on-time the switch remains off until the FB voltage falls below the reference,but never before the minimum off-time forced by the minimum off-time one-shot timer.When the FB pin voltage falls below the reference and the minimum off-time one-shot period expires,the buck switch is turned on for another on-time one-shot period.This will continue until regulation is achieved and the FB voltage is approximately equal to 1.225V (typ).8Submit Documentation FeedbackCopyright ©2012,Texas Instruments IncorporatedProduct Folder Links:LM25017VOUTVOUT(low ripple)VOUTVOUT (low ripple)R FB2 + R FB1V OUT = 1.225V xR FB1V OUT g sw =10-10x R ONLM25017SNVS951–DECEMBER 2012In a synchronous buck converter,the low side (sync)FET is ‘on’when the high side (buck)FET is ‘off’.The inductor current ramps up when the high side switch is ‘on’and ramps down when the high side switch is ‘off’.There is no diode emulation feature in this IC,and therefore,the inductor current may ramp in the negative direction at light load.This causes the converter to operate in continuous conduction mode (CCM)regardless of the output loading.The operating frequency remains relatively constant with load and line variations.The operating frequency can be calculated as follows:(1)The output voltage (V OUT )is set by two external resistors (R FB1,R FB2).The regulated output voltage is calculated as follows:(2)(3)This regulator regulates the output voltage based on ripple voltage at the feedback input,requiring a minimum amount of ESR for the output capacitor (C OUT ).A minimum of 25mV of ripple voltage at the feedback pin (FB)is required for the LM25017.In cases where the capacitor ESR is too small,additional series resistance may be required (R C in Figure 13Low Ripple Output Configuration).For applications where lower output voltage ripple is required the output can be taken directly from a low ESR output capacitor,as shown in Figure 13Low Ripple Output Configuration.However,R C slightly degrades the load regulation.V CC RegulatorThe LM25017contains an internal high voltage linear regulator with a nominal output of 7.6V.The input pin (V IN )can be connected directly to the line voltages up to 48V.The V CC regulator is internally current limited to 30mA.The regulator sources current into the external capacitor at V CC .This regulator supplies current to internal circuit blocks including the synchronous MOSFET driver and the logic circuits.When the voltage on the V CC pin reaches the undervoltage lockout (V CC UVLO)threshold of 4.5V,the IC is enabled.The V CC regulator contains an internal diode connection to the BST pin to replenish the charge in the gate drive boot capacitor when SW pin is low.At high input voltages,the power dissipated in the high voltage regulator is significant and can limit the overall achievable output power.As an example,with the input at 48V and switching at high frequency,the V CC regulator may supply up to 7mA of current resulting in 48V x 7mA =336mW of power dissipation.If the V CC voltage is driven externally by an alternate voltage source,between 8V and 13V,the internal regulator is disabled.This reduces the power dissipation in the IC.Figure 13.Low Ripple Output ConfigurationCopyright ©2012,Texas Instruments Incorporated Submit Documentation Feedback9Product Folder Links:LM250170.07 x V INT OFF(ILIM) =V FB + 0.2VP s10-10 x R ONT ON =V INLM25017SNVS951–DECEMBER 2012Regulation ComparatorThe feedback voltage at FB is compared to an internal 1.225V reference.In normal operation,when the output voltage is in regulation,an on-time period is initiated when the voltage at FB falls below 1.225V.The high side switch will stay on for the on-time,causing the FB voltage to rise above 1.225V.After the on-time period,the high side switch will stay off until the FB voltage again falls below 1.225V.During start-up,the FB voltage will be below 1.225V at the end of each on-time,causing the high side switch to turn on immediately after the minimum forced off-time of 144ns.The high side switch can be turned off before the on-time is over,if the peak current in the inductor reaches the current limit threshold.Overvoltage ComparatorThe feedback voltage at FB is compared to an internal 1.62V reference.If the voltage at FB rises above 1.62V the on-time pulse is immediately terminated.This condition can occur if the input voltage and/or the output load changes suddenly.The high side switch will not turn on again until the voltage at FB falls below 1.225V.On-Time GeneratorThe on-time for the LM25017is determined by the R ON resistor,and is inversely proportional to the input voltage (V IN ),resulting in a nearly constant frequency as V IN is varied over its range.The on-time equation for the LM25017is:(4)See figure “T ON vs V IN and R ON ”in the section “Performance Curves”.R ON should be selected for a minimum on-time (at maximum V IN )greater than 100ns,for proper operation.This requirement limits the maximum switching frequency for high V IN .Current LimitThe LM25017contains an intelligent current limit off-timer.If the current in the buck switch exceeds 1.02A the present cycle is immediately terminated,and a non-resetable off-timer is initiated.The length of off-time is controlled by the FB voltage and the input voltage V IN .As an example,when FB =0V and V IN =48V,the maximum off-time is set to 16μs.This condition occurs when the output is shorted,and during the initial part of start-up.This amount of time ensures safe short circuit operation up to the maximum input voltage of 48V.In cases of overload where the FB voltage is above zero volts (not a short circuit)the current limit off-time is reduced.Reducing the off-time during less severe overloads reduces the amount of foldback,recovery time,and start-up time.The off-time is calculated from the following equation:(5)The current limit protection feature is peak limited.The maximum average output will be less than the peak.N-Channel Buck Switch and DriverThe LM25017integrates an N-Channel Buck switch and associated floating high voltage gate driver.The gate driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode.A 0.01uF ceramic capacitor connected between the BST pin and the SW pin provides the voltage to the driver during the on-time.During each off-time,the SW pin is at approximately 0V,and the bootstrap capacitor charges from V CC through the internal diode.The minimum off-timer,set to 144ns ,ensures a minimum time each cycle to recharge the bootstrap capacitor.Synchronous RectifierThe LM25017provides an internal synchronous N-Channel MOSFET rectifier.This MOSFET provides a path for the inductor current to flow when the high-side MOSFET is turned off.The synchronous rectifier has no diode emulation mode,and is designed to keep the regulator in continuous conduction mode even during light loads which would otherwise result in discontinuous operation.10Submit Documentation FeedbackCopyright ©2012,Texas Instruments IncorporatedProduct Folder Links:LM25017LM25017 SNVS951–DECEMBER2012Undervoltage DetectorThe LM25017contains a dual level undervoltage lockout(UVLO)circuit.When the UVLO pin voltage is below 0.66V,the controller is in a low current shutdown mode.When the UVLO pin voltage is greater than0.66V but less than1.225V,the controller is in standby mode.In standby mode the V CC bias regulator is active while the regulator output is disabled.When the V CC pin exceeds the V CC undervoltage threshold and the UVLO pin voltage is greater than1.225V,normal operation begins.An external set-point voltage divider from V IN to GND can be used to set the minimum operating voltage of the regulator.UVLO hysteresis is accomplished with an internal20μA current source that is switched on or off into the impedance of the set-point divider.When the UVLO threshold is exceeded,the current source is activated to quickly raise the voltage at the UVLO pin.The hysteresis is equal to the value of this current times the resistance R UV2.UVLO V CC Mode Description<0.66V Shutdown V CC regulator disabled.Switcher disabled.0.66V–1.225V Standby V CC regulator enabledSwitcher disabled.>1.225V V CC<4.5V Standby V CC regulator enabled.Switcher disabled.V CC>4.5V Operating V CC enabled.Switcher enabled.If the UVLO pin is wired directly to the V IN pin,the regulator will begin operation once the V CC undervoltage is satisfied.Figure14.UVLO Resistor SettingThermal ProtectionThe LM25017should be operated so the junction temperature does not exceed150°C during normal operation. An internal Thermal Shutdown circuit is provided to protect the LM25017in the event of a higher than normal junction temperature.When activated,typically at165°C,the controller is forced into a low power reset state, disabling the buck switch and the V CC regulator.This feature prevents catastrophic failures from accidental device overheating.When the junction temperature reduces below145°C(typical hysteresis=20°C),the V CC regulator is enabled,and normal operation is resumed.Application InformationSELECTION OF EXTERNAL COMPONENTSSelection of external components is illustrated through a design example.The design example specifications are as follows:Buck Converter Design SpecificationsInput voltage range12.5V to48VOutput voltage10VMaximum Load current500mASwitching Frequency200kHzCopyright©2012,Texas Instruments Incorporated Submit Documentation Feedback11Product Folder Links:LM25017ûI LC OUT =8 x g sw x ûV rippleûI L(MAX)I LI (peak) = I OUT +2= 590 mA V IN - V OUT ûI L =L1 x g SWV OUTV IN xV OUT g SW =K x R OND MIN g SW(MAX) =T ON(MIN)10/48100 ns== 2.1 MHz1 - D MAX g SW(MAX) =T OFF(MIN)1 - 10/12.5200 ns == 1 MHzLM25017SNVS951–DECEMBER 2012RFB1,RFB2:V OUT =V FB x (R FB2/R FB1+1),and since V FB =1.225V,the ratio of R FB2to R FB1calculates as 7:1.Standard values of 6.98k Ωand 1.00k Ωare chosen.Other values could be used as long as the 7:1ratio is maintained.Frequency Selection:At the minimum input voltage,the maximum switching frequency of LM25017is restricted by the forced minimum off-time (T OFF(MIN))as given by:(6)Similarly,at maximum input voltage,the maximum switching frequency of LM25017is restricted by the minimumT ON as given by:(7)Resistor R ON sets the nominal switching frequency based on the following equations:(8)where K =1x 10–10.Operation at high switching frequency results in lower efficiency while providing the smallest solution.For this example a conservative 200kHz was selected,resulting in R ON =504k Ω.Selecting a standard value for R ON =499k Ωresults in a nominal frequency of 202kHz.Inductor Selection:The minimum inductance is selected to limit the output ripple to 20to 40percent of the maximum load current.In addition,the peak inductor current at maximum load should be smaller than the minimum current limit as given in electrical characteristics table.The inductor current ripple is given by:(9)The maximum ripple is observed at maximum input voltage.Substituting V IN =48V and ΔIL =40percent x I OUT(max)results in L1=197μH.The next higher standard value of 220μH is chosen.The peak-to-peak minimum and maximum inductor current ripples of 35mA and 179mA are given at minimum and maximum input voltages respectively.The peak inductor and switch current is given by(10)which is smaller than the minimum current limit.The inductor should be able to withstand the maximum current limit of 1.3A,which can be reached during startup and overload conditions.Figure 15.Reference Schematic for Selection of External ComponentsOutput Capacitor:The output capacitor is selected to minimize the capacitive ripple across it.The maximum ripple is observed at maximum input voltage and is given by:(11)12Submit Documentation FeedbackCopyright ©2012,Texas Instruments IncorporatedProduct Folder Links:LM25017R UV2V IN (UVLO,rising) = 1.225V x R UV1+ 1()V IN (HYS)=I HYS x R UV2I OUT(MAX)C IN 8 x g SW x ûV IN>25 mV R C ûI L(MIN)V OUTV REFx>LM25017SNVS951–DECEMBER 2012where ΔV ripple is the voltage ripple across the capacitor.Substituting ΔV ripple =10mV gives C OUT =12.64μF.A 22μF standard value is selected.An X5R or X7R type capacitor with a voltage rating 16V or higher should be selected.Series Ripple Resistor R C :The series resistor should be selected to produce sufficient ripple at the feedback node.The ripple produced by R C is proportional to the inductor current ripple,and therefore R C should be chosen for minimum inductor current ripple which occurs at minimum input voltage.The R C is calculated by the equation:(12)This gives an R C of greater than or equal to 5.15Ω.Selecting R C =5.23Ωresults in ~1V of maximum output voltage ripple.For applications requiring lower output voltage ripple,Type II or Type III ripple injection circuits should be used as described in the section “Ripple Configuration”.V CC and Bootstrap Capacitor:The V CC capacitor provides charge to bootstrap capacitor as well as internal circuitry and low side gate driver.The Bootstrap capacitor provides charge to high side gate driver.A good value for CV CC is 1μF.A good value for C BST is 0.01μF.Input Capacitor:Input capacitor should be large enough to limit the input voltage ripple:(13)choosing a ΔV IN =0.5V gives a minimum C IN =1.24μF.A standard value of 2.2μF is selected.The input capacitor should be rated for the maximum input voltage under all conditions.A 50V,X7R dielectric should be selected for this design.Input capacitor should be placed directly across V IN and RTN (pin 2and 1)of the IC.If it is not possible to place all of the input capacitor close to the IC,a 0.47μF capacitor should be placed near the IC to provide a bypass path for the high frequency component of the switching current.This helps limit the switching noise.UVLO Resistors:The UVLO resistors R FB1and R FB2set the UVLO threshold and hysteresis according to the following relationship:(14)and(15)where I HYS =20μA.Setting UVLO hysteresis of 2.5V and UVLO rising threshold of 12V results in R UV1=14.53k Ωand R UV2=125k Ω.Selecting standard value of R UV1=14k Ωand R UV2=125k Ωresults in UVLO thresholds and hysteresis of 12.4V and 2.5V respectively.APPLICATION CIRCUIT:12V TO 48V INPUT AND 10V,500mA OUTPUT BUCK CONVERTERThe application schematic of a buck supply is shown in Figure 16below.For output voltage (V OUT )above the maximum regulation threshold of V CC (8.55V,see electrical characteristics),the V CC pin can be connected to V OUT through a diode (D2),as shown below,for higher efficiency and lower power dissipation in the IC.Copyright ©2012,Texas Instruments Incorporated Submit Documentation Feedback13Product Folder Links:LM25017N SV OUT2 = V OUT1 xN P- V FLM25017SNVS951–DECEMBER 2012Figure 16.Final Schematic for 12V to 48V Input,and 10V,500mA Output Buck ConverterISOLATED DC-DC CONVERTER USING LM25017An isolated supply using LM25017is shown in Figure 17below.Inductor (L)in a typical buck circuit is replaced with a coupled inductor (X1).A diode (D1)is used to rectify the voltage on a secondary output.The nominal voltage at the secondary output (V OUT2)is given by:(16)where VF is the forward voltage drop of D1,and NP,NS are the number of turns on the primary and secondary of coupled inductor X1.For output voltage (V OUT1)above the maximum V CC (8.55V),the V CC pin can be diode connected to V OUT1for higher efficiency and low dissipation in the IC.See AN-2292for a complete isolated bias design.Figure 17.Typical Isolated Application SchematicRIPPLE CONFIGURATIONLM25017uses Constant-On-Time (COT)control scheme,in which the on-time is terminated by an on-timer,and the off-time is terminated by the feedback voltage (V FB )falling below the reference voltage (V REF ).Therefore,for stable operation,the feedback voltage must decrease monotonically,in phase with the inductor current during the off-time.Furthermore,this change in feedback voltage (V FB )during off-time must be large enough to suppress any noise component present at the feedback node.Table 1shows three different methods for generating appropriate voltage ripple at the feedback node.Type 1and Type 2ripple circuits couple the ripple at the output of the converter to the feedback node (FB).The output voltage ripple has two components:1.Capacitive ripple caused by the inductor current ripple charging/discharging the output capacitor.2.Resistive ripple caused by the inductor current ripple flowing through the ESR of the output capacitor.14Submit Documentation FeedbackCopyright ©2012,Texas Instruments IncorporatedProduct Folder Links:LM25017。